The present invention relates to the field of medical monitoring devices. More particularly, the present invention relates to cardiac pacing systems that provide a method for monitoring heart failure based on the speed of rate changes in the hemodynamic performance of the heart.
Heart failure is a disease that may be characterized by such symptoms as left ventricular dysfunction, arrhythmias, pulmonary and peripheral congestion, fatigue and shortness of breath. In earlier stages, patients may not be able to perform strenuous activities and, in later stages, may not even be able to perform routine activities such as climbing the stairs. Furthermore, the relationship between inability to perform strenuous activities and the corresponding state of the patient""s heart may be difficult to discern and quantify.
Close monitoring of patients who experience heart failure or who are determined to be at risk for heart failure may be desirable. However, such monitoring presents some difficulties. For example, each patient""s heart differs from that of another patient. One patient in earlier stages of heart failure may have a different activity profile than another, more physically fit patient, in the same stage of heart failure. Additionally, external methods of monitoring heart failure in a patient may be awkward. For example, a patient may seem to be in one stage of heart failure while being assessed at his physician""s office while in fact, his actual everyday activities would indicate he is in a completely different stage of heart failure. Moreover, invasive methods of more closely examining a patient""s stage of heart failure may not be desirable in all patients, such as those who are in reasonably early stages.
Some patients with a history of heart failure are treated with implantable pulse generators, such as pacemakers. Implantable pulse generators (IPGs) are well known in the art. As these IPGs are already implanted within the patient and providing cardiac data, it may be desirable to use such devices to determine the status of heart failure in such patients.
In particular, it may be desirable to monitor a heart failure patient in order to determine that his hemodynamic performance is sufficient under conditions of stress, such as exercise. The heart rate""s response to such conditions depends on the hemodynamic performance of the heart. A pronounced increase in heart rate may well indicate low hemodynamic performance. That is, a heart rate that increases at a very high speed may indicate deteriorated pumping function, which in turn, may indicate, heart failure. However, the hemodynamic performance will be individual to each patient, particularly because other parameters, such as physical fitness, affect the speed at which heart rate changes.
Thus, a need exists in the medical arts for monitoring heart failure in a patient based on the speed at which the heart rate accelerates or decelerates in comparison to an individualized baseline value.
Some methods have been proposed in the prior art for measuring heart failure based on heart rate.
For example, U.S. Pat. Nos. 5,749,900 and 6,035,233 to Schroeppel et al. describe methods of measuring variability in heart rate and comparing the measured heart rate variability to a stored variability zone. Selective therapy regimes may be initiated depending on the heart rate variability measurement.
U.S. Pat. Nos. 5,148,812; 5,265,617; 5,437,285; 5,560,370; 5,842,997; 5,921,940 to Verrier, et al. describe methods of measuring cardiac vulnerability based on T-wave alternans analysis, simultaneous analysis of T-wave alternans and heart rate variability analysis, simultaneous assessment of autonomic function and cardiac electrical stability, simultaneous assessment of T-wave alternans and QT interval dispersion and assessment of physiological stress.
U.S. Pat. No. 6,045,513 to Stone et al. describes use of an IPG to monitor a patient""s functional status.
U.S. Pat. No. 4,832,038 to Arai et al. describes use of power spectral analysis of heart rate to monitor cardiovascular regulation.
U.S. Pat. No. 4,862,361 to Gordon et al. also describes use of power spectral analysis of heart rate to monitor cardiovascular regulation.
The most pertinent prior art patents known are the present time are shown in the following table:
The patents listed in Table 1 are hereby incorporated by reference herein, each in its entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, at least some of the devices and methods disclosed in the patent of Table 1 may be modified advantageously in accordance with the teachings of the present invention.
The present invention is therefore directed to providing a method and system for monitoring heart failure based on the speed at which the patient""s heart rate accelerates or decelerates compared to an individualized baseline value. The system of the present invention overcomes at least some of the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of monitoring heart failure in a patient.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the pacing of cardiac tissue. Those problems include, without limitation: (a) difficulty in monitoring the functional status of heart failure patients; (b) individual variation in the hemodynamic performance of different patients with heart failure; (c) difficulty in obtaining an indication of heart failure as patient""s physical fitness changes; and (d) difficulty in determining an appropriate indication of heart failure for a particular patient.
In comparison to known pacing techniques, various embodiments of the present invention provide one or more of the following advantages: (a) monitoring heart failure in a patient based on the speed at which heart rate changes; (b) ability to obtain an indication of heart failure that is unique to each patient (c) ability to determine a baseline value for monitoring heart failure, and (d) ability to monitor trends over time in a heart failure patient.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of monitoring heart failure in a patient; (b) an IPG capable of measuring rate dynamics in a patient; (c) methods of monitoring heart failure in a patient based on the speed at which the heart rate changes; (d) methods of setting individualized baseline values for monitoring the hemodynamic performance of a particular patient.
At least some embodiments of the present invention involve determining a baseline heart rate change value which reflects the speed at which a first initial heart rate changes to a second initial heart rate. At least one subsequent heart rate change value is determined which reflects the speed at which a first subsequent heart rate changes to a second subsequent heart rate. The subsequent heart rate change value may be compared to the baseline heart rate change to obtain at least one heart failure value. Several subsequent heart rates may be measured and several subsequent heart rate change values may be calculated. Two immediately subsequent heart rates may be compared to each other to achieve a subsequent heart rate change value. Alternatively, a given heart rate may be compared to any previous heart rate to determine a subsequent heart rate change values. Average, maximum, minimum heart rate change values may be determined for a given patient and stored or evaluated over time.